1. Field of the Invention
The present invention relates to a microarray substrate, a method of use, and products, e.g., a microarray and Lab-On-a-Chip (LOC) system, comprising the microarray substrate.
2. Description of the Related Art
A microarray refers to a high-density array of molecules immobilized in predetermined regions of a substrate. One way in which a microarray can be classified is based on the molecule immobilized on the substrate, e.g, a polynucleotide microarray, a protein microarray, etc. The term “polynucleotide microarray” refers to a high-density array of polynucleotides immobilized in predetermined regions of a substrate. Such microarrays are well known in the art. Examples of such microarrays are disclosed in U.S. Pat. Nos. 5,445,934 and No. 5,744,305.
Immobilization of polynucleotides on a solid substrate can be achieved by direct synthesis of polynucleotides on the solid substrate or by deposition of polynucleotides on predetermined regions of the solid substrate (spotting method). Illustrative methods for manufacturing such polynucleotide microarrays are disclosed in U.S. Pat. Nos. 5,744,305, 5,143,854, and No. 5,424,186.
The spotting method has been widely used for covalent attachment of biomolecules on solid substrates. For example, one widely used method of immobilizing biomolecules on a solid substrate includes: activating a surface of the solid substrate by introducing a nucleophilic functional group (e.g., an amino group) on the solid substrate, coupling biomolecules (e.g., polynucleotides) activated with a good leaving group to the surface-activated solid substrate, and removing any unreacted reactants. Drawbacks of this method include low attachment efficiency of polynucleotides to the coated surface and non-specific binding of target molecules to the coated surface or binding of impurities in the target sample to the coated surface.
Meanwhile, pH-dependent ion-exchange materials have been used in the separation of nucleic acids. For example, U.S. Patent Publication No. 2001/0018513 discloses a method of isolating a nucleic acid using a material having an ionizable group. The material is positively charged at a first pH to permit nucleic acid binding to the material; the bound nucleic acid is released from the material at a second pH higher than the first pH. Examples of such a material having an ionizable group include N-2-acetamido-2-aminoethanesulfonic acid (ACES), N-2-acetamido-2-imidodiacetic acid (ADA), N-trihydroxymethyl-methyl-2-aminoethanesulfonic acid (TES), and trihydroxymethylaminoethane. Additionally, U.S. Pat. No. 6,310,199 discloses a method of isolating a nucleic acid using a pH-dependent ion-exchange material including a silica magnetic particle and a plurality of ion-exchange ligands. Each ion exchange ligand comprises an aromatic hydrocarbon ring; a spacer covalently attached to the aromatic hydrocarbon ring; and a linker including a linker alkyl chain attached to the silica magnetic particle at a first end of the linker alkyl chain and attached to the spacer at a second end of the linker alkyl chain.
The present inventors have studied coating materials applicable to the solid substrate of a microarray substrate and have discovered that coating a microarray substrate with a pH-dependent ion-exchange material helps to solve the aforementioned problems of the prior art.